Dataset Information

Thermodynamics of porphyrin dimerization in aqueous solutions.

ABSTRACT: The dimerization equilibrium of deuteroporphyrin IX and of mesoporphyrin IX in aqueous solutions were studied by fluorimetric techniques over the 0.01-1 microM concentration range, where dimerization is the dominant aggregation process. Deuteroporphyrin IX was studied at several temperatures over the range 22-37 degrees C, and mesoporphyrin at 25 and 37 degrees C. The magnitudes determined for the dimerization equilibrium constants (25 degrees C, neutral pH, phosphate-buffered saline) are 2.3 X 10(6)M-1 and 5.4 X 10(6)M-1 for the deutero and meso derivatives respectively. The meso, deutero and haemato species tested show a similar temperature effect, namely dimerization decreasing with increasing temperature, indicating the involvement of a negative enthalpy change. Van't Hoff isochore of the dimerization constants determined for deuteroporphyrin IX was linear within the temperature range of 22-37 degrees C, allowing the calculation of the thermodynamic parameters. For deuteroporphyrin dimerization, those were found to be delta G0 = -36. 4kJ X mol-1; delta H0 = -46. 0kJ X mol-1 and delta S0 = -32.2J X K-1 X mol-1 (at neutral pH, 25 degrees C, phosphate-buffered saline), showing the process to be enthalpy-driven. Similar trends have been found for porphyrin species other than those studied here. Our data fit with a hypothesis giving a major role to the solvent in driving porphyrins to aggregate in aqueous solution. The magnitudes and directions of the energetic changes fit better with the expectation of the ' solvophobic force' theory predicting enthalpy-driven association, than with the classic hydrophobic bonding, predicting the association to be entropy-driven.

SUBMITTER: Margalit R

PROVIDER: S-EPMC1153501 | biostudies-other | 1984 Apr

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Motivated by the possibility of enhancing aerosol drug delivery to mucus-obstructed lungs, the spreading of a drop of aqueous surfactant solution on a physically entangled aqueous poly(acrylamide) solution subphase that mimics lung airway surface liquid was investigated. Sodium dodecyl sulfate was used as the surfactant. To visualize spreading of the drop and mimic the inclusion of a drug substance, fluorescein, a hydrophilic and non-surface-active dye, was added to the surfactant solution. The spreading progresses through a series of events. Marangoni stresses initiate the convective spreading of the drop. Simultaneously, surfactant escapes across the drop's contact line within a second of deposition and causes a change in subphase surface tension outside the drop on the order of 1 mN/m. Convective spreading of the drop ends within 2-3 s of drop deposition, when a new interfacial tension balance is achieved. Surfactant escape depletes the drop of surfactant, and the residual drop takes the form of a static lens of nonzero contact angle. On longer time scales, the surfactant dissolves into the subphase. The lens formed by the water in the deposited drop persists for as long as 3 min after the convective spreading process ends due to the long diffusional time scales associated with the underlying entangled polymer solution. The persistence of the lens suggests that the drop phase behaves as if it were immiscible with the subphase during this time period. Whereas surfactant escapes the spreading drop and advances on the subphase/vapor interface, hydrophilic dye molecules in the drop do not escape but remain with the drop throughout the convective spreading. The quasi-immiscible nature of the spreading event suggests that the chemical properties of the surfactant and subphase are much less important than their physical properties, consistent with prior qualitative studies of spreading of different types of surfactants on entangled polymer subphases: the selection of surfactant for pulmonary delivery applications may be limited only by physical and toxicological considerations. Further, the escape of surfactant from individual drops may provide an additional spreading mechanism in the lung, as hydrodynamic and/or surface pressure repulsions may drive individual droplets apart after deposition.

Dataset Information

Thermodynamics of porphyrin dimerization in aqueous solutions.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure